(1) On magnetic media, a condition in which the magnetizable particles are completely aligned and a more powerful writing signal will not improve the reading back.
(2) In a bipolar transistor, a condition in which the current on the gate (the trigger) is equal to or greater than what is necessary to close the switch.
(3) In a diode, a condition in which the diode is fully conducting.
(4) In a color, the amount of pure pigment it contains. For example, a fully saturated red would be pure red. The less saturated, the more pastel the appearance. See HSB, HSL, chroma, luminance and hue.